190 Things not generally Known. 



andi, as practised by the Kaffirs of South Africa, is thus de- 

 scribed by Captain Drayton : 



Two dry sticks, one being of hard and the other of soft wood, were 

 the materials used. The soft stick was laid on the ground, and held 

 firmly down by one Kaffir, whilst another employed himself in scooping 

 out a little hole in the centre of it with the point of his assagy : into this 

 little hollow the end of the hard wood was placed, and held vertically. 

 These two men sat face to face, one taking the vertical stick between 

 the palms of his hands, and making it twist about very quickly, while 

 the other Kaffir held the lower stick firmly in its place ; the friction 

 caused by the end of one piece of wood revolving upon the other soon 

 made the two pieces smoke. When the Kaffir who twisted became tired, 

 the respective duties were exchanged. These operations having conti- 

 nued about a couple of minutes, sparks began to appear, and when they 

 became numerous, were gathered into some dry grass, which was then 

 swung round at arm's length until a blaze was established ; and a roar- 

 ing fire was gladdening the hearts of the Kaffirs with the anticipation of 

 a glorious feast in about ten minutes from the time that the operation 

 was first commenced. 



HEAT BY FEICTION FEOM ICE. 



When Sir Humphry Davy was studying medicine at Pen- 

 zance, one of his constant associates was Mr. Tom Harvey, a 

 druggist in the above town. They constantly experimented to- 

 gether ; and one severe winter's day, after a discussion on the 

 nature of heat, the young philosophers were induced to go to 

 Larigan river, where Davy succeeded in developing heat by rub- 

 bing two pieces of ice together so as to melt each other ;* an ex- 

 periment which he repeated with much eclat many years after, 

 in the zenith of his celebrity, at the Royal Institution. The 

 pieces of ice for this experiment are fastened to the ends of two 

 sticks, and rubbed together in air below the temperature of 

 32 : this Davy readily accomplished on the day of severe cold 

 at the Larigan river ; but when the experiment was repeated at 

 the Royal Institution, it was in the vacuum of an air-pump, 

 when the temperature of the apparatus and of the surrounding 

 air was below 32. It was remarked, that when the surface 

 of the rubbing pieces was rough, only half as much heat was 

 evolved as when it was smooth. When the pressure of the rub- 

 bing piece was increased four times, the proportion of heat 

 evolved was increased sevenfold. 



WAEMING WITH ICE. 



In common language, any thing is understood to be cooled 

 or warmed when the temperature thereof is made higher or 

 lower, whatever may have been the temperature when the 

 change was commenced. Thus it is said that melted iron is 



* Could we by mechanical pressure force water into a solid state, an immense 

 nantity of he<it would be set free. 



